1. Field of the Invention
The present invention relates to a nonreciprocal circuit device for use in, for example, a microwave band and also relates to a communication apparatus including such a nonreciprocal circuit device.
2. Description of the Related Art
An exemplary isolator, which is a nonreciprocal circuit device, according to the related art will now be described with reference to FIGS. 11, 12A, and 12B.
FIG. 11 is an exploded perspective view of an isolator according to the related art, FIG. 12A is a sectional plan thereof, and FIG. 12B is an equivalent circuit diagram thereof.
Referring to FIGS. 11, 12A, and 12B, reference numeral 1 indicates a ferrite member, 2 generally indicates center conductors (2a is a center conductor for an input port, 2b is a center conductor for an output port, and 2c is a center conductor for a terminating port), 3 is a magnetic assembly, 4 is a housing, 5 is an upper yoke, 6 is a permanent magnet, 7 is a spacer, 8 is a lower yoke, 9 is an input terminal, 10 is an output terminal, 11 are ground terminals, R is a resistor, C1, C2, and C3 are capacitors, and H indicates the direction of a magnetic field applied to the ferrite member 1.
The center conductors 2 are defined by the center conductor 2a for an input port (input-port center conductor 2a), the center conductor 2b for an output port (output-port center conductor 2b), and the center conductor 2c for a terminating port (terminating-port center conductor 2c). The center conductors 2a to 2c are arranged so as to cross one another on the ferrite member 1. The center conductors 2a to 2c and the ferrite member 1 define the magnetic assembly 3.
The housing 4 is provided with the lower yoke 8, the input terminal 9, the output terminal 10, and the plurality of ground terminals 11. The housing 4 accommodates the magnetic assembly 3, the permanent magnet 6 for applying a static magnetic field to the magnetic assembly 3, the spacer 7 separating the magnetic assembly 3 and the permanent magnet 6, the capacitors C1, C2, and C3, which define matching elements, and the resistor R, which defines a terminating resistor. The upper yoke 5 covers the upper portion of the housing 4.
In the housing 4, the capacitor C3 and the resistor R are connected to one end of the terminating-port center conductor 2c. The capacitors C1 and C2 are connected to the input-port center conductor 2a and the output-port center conductor 2b, respectively. The center conductors 2a to 2c, the capacitors C1 to C3, and the resistor R are connected to the corresponding ground terminals 11 provided in the housing 4. An input port 109 is arranged such that one end of the input-port center conductor 2a is connected to the input terminal 9 and the capacitor C1 is connected between the one end of the input-port center conductor 2a and the corresponding ground terminal 11. An output port 110 is arranged such that one end of the output-port center conductor 2b is connected to the output terminal 10 and the capacitor C2 is connected between the one end of the output-port center conductor 2b and the corresponding ground terminal 11. In addition, a terminating port 111 is arranged such that the capacitor C3 and the resistor R are connected in parallel between the terminating-port center conductor 2c and the corresponding ground terminals 11.
In this state, an electromagnetic wave entering from the input terminal 9 is output from the output terminal 10, while an electromagnetic wave entering from the output terminal 10 is absorbed by the resistor R of the terminating port 111, and thus, is not output to the input terminal 9, thereby functioning as an isolator.
However, such a nonreciprocal circuit device of the related art has the following deficiencies.
Typically, in a mobile communication apparatus, and particularly a battery-operated communication apparatus, such as a portable communication apparatus, active elements such as a transistor for a power amplifier, are operated by, for example, a power supply having a low voltage of about 3 V to about 4.5 V. When 1 watt of power is required in such a low voltage operation, the load impedance of the active element is about 3xcexa9 to about 5xcexa9. On the other hand, an antenna, antenna duplexer, and switch are typically configured to have a characteristic impedance of about 50xcexa9.
An isolator, which defines a nonreciprocal circuit device, is provided adjacent to the output of the power amplifier, and is used to prevent an increase in power consumption due to stabilizing the operation of the radio wave transmitter or inhibiting load fluctuation, or to prevent the output distortion factor from deteriorating. In this case, since the isolator is configured to have a characteristic impedance of about 50xcexa9, the power amplifier to be connected to the isolator must include a circuit for converting the 3xcexa9 to 5xcexa9 impedance of the active element of the isolator to the 50xcexa9 impedance of the isolator, such that the return loss does not increase at the input of the isolator. Thus, such a converter circuit has commonly been provided inside or outside a power amplifier. However, the converter circuit experiences problems such as transmission loss, a reduced operating frequency band, and an increased size (required for the space of the converter circuit).
In order to overcome the problems described above, preferred embodiments of the present invention provide a compact and low-loss nonreciprocal circuit device that permits direct connection of a low impedance element to the input port without providing an impedance converter circuit, and that permits connection of a low impedance element having a greatly simplified matching circuit as compared to the related art to the input port. Also, other preferred embodiments of the present invention provide a communication apparatus including such a novel nonreciprocal circuit device.
According to a preferred embodiment of the present invention, a nonreciprocal circuit device includes a magnetic assembly in which a center conductor for an input port and center conductors for the other ports are disposed on a ferrite member so as to cross one another. The nonreciprocal circuit device further includes a permanent magnet for applying a static magnetic field to the magnetic assembly, and matching circuits connected to the corresponding center conductors. When the center conductors for the input port and the other ports are viewed as lines, the characteristic impedance of the center conductor for the input port is less than the characteristic impedance of the center conductors for the other ports. This arrangement provides a low-loss wide-band nonreciprocal circuit device having a low input-impedance.
Thus, even when a low-impedance circuit element (e.g., a power amplifier) is connected to a stage prior to the nonreciprocal circuit device, low-loss signal transmission is achieved.
Preferably, the matching circuit connected to the center conductor for the input port includes a series capacitor connected in series to the center conductor for the input port and a parallel capacitor connected between the center conductor for the input port and a ground electrode. This arrangement provides a nonreciprocal circuit device having greatly improved characteristics of impedance matching, input return loss, isolation, and insertion loss over the wider frequency band.
Preferably, the width of the center conductor for the input port is greater than the width of the center conductors for the other ports. This configuration provides a low-loss, wide-band nonreciprocal circuit device having a low input-impedance.
The center conductor for the input are preferably defined by a single conductor element that extends in the width direction thereof, and the center conductors for the other ports are each preferably defined by a plurality of conductor elements that are substantially parallel to each other. The width of the single conductor element defining the center conductor for the input port is preferably greater than the combined total width of the conductor elements defining each of the center conductors for the other ports. This configuration provides a low-loss, wide-band nonreciprocal circuit device having a low input-impedance.
Each of the center conductors for the input port and for the other ports may be defined by a plurality of conductor elements that are substantially parallel to each other. The number of conductor elements defining the center conductor for the input port is greater than the number of conductor elements defining each of the center conductors for the other ports. The combined total width of the conductor elements defining the center conductor for the input port is preferably greater than the combined total width of the conductor elements defining each of the center conductors for the other ports. This configuration provides a low-loss, wide-band nonreciprocal circuit device having a low input-impedance.
Preferably, the center conductor for the input port has a thickness that is greater than the thickness of the center conductors for the other ports. This configuration provides a low-loss, wide-band nonreciprocal circuit device having a low input-impedance. In addition, this arrangement achieves a low input-impedance without varying the width of any of the conductor elements.
Preferably, the characteristic impedance of the center conductor for the input port is about 3xcexa9 to about 30xcexa9. With this arrangement, even when the nonreciprocal circuit device is directly connected to a power amplifier circuit and a filter circuit, or is connected to a power amplifier and a filter having a simplified and low-loss matching circuit as compared to a conventionally-used matching circuit, low-loss signal transmission is achieved.
Preferably, the characteristic impedance of the center conductors for the other ports is about 50xcexa9. This allows matching with elements, such as an antenna duplexer and antenna, of a communication system, to thereby achieve a low-loss signal transmission. Additionally, this arrangement provides an output return loss characteristic having an increased frequency band.
Preferably, one of the center conductors for the other ports is terminated. This arrangement provides a low-loss isolator.
According to another preferred embodiment of the present invention, a communication apparatus is provided that includes the nonreciprocal circuit device according to the first preferred embodiment of the present invention. This provides a communication apparatus having greatly reduced transmission loss.
Other feature, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.